netdev - Re: stmmac smatch error rx_queue

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Date:   Mon, 22 Jan 2018 16:55:10 +0000
From:   Jose Abreu <Jose.Abreu@...opsys.com>
To:     Niklas Cassel <niklas.cassel@...s.com>, <peppe.cavallaro@...com>,
        <alexandre.torgue@...com>, <Joao.Pinto@...opsys.com>,
        <Jose.Abreu@...opsys.com>
CC:     <netdev@...r.kernel.org>
Subject: Re: stmmac smatch error rx_queue_routing

Hi Niklas,

On 22-01-2018 16:43, Niklas Cassel wrote:
> Hello stmmac peeps,
>
> I found this smatch error:
>
> drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c:132 dwmac4_tx_queue_routing() error:
>   buffer overflow 'route_possibilities' 5 <= 254
> drivers/net/ethernet/stmicro/stmmac/dwmac4_core.c:133 dwmac4_tx_queue_routing() error:
>   buffer overflow 'route_possibilities' 5 <= 254
>
> Looking at the code raises some questions:
>
>
> static void dwmac4_tx_queue_routing(struct mac_device_info *hw,
>                                     u8 packet, u32 queue)
> {
>         ...
>         static const struct stmmac_rx_routing route_possibilities[] = {
>                 { GMAC_RXQCTRL_AVCPQ_MASK, GMAC_RXQCTRL_AVCPQ_SHIFT },
>                 { GMAC_RXQCTRL_PTPQ_MASK, GMAC_RXQCTRL_PTPQ_SHIFT },
>                 { GMAC_RXQCTRL_DCBCPQ_MASK, GMAC_RXQCTRL_DCBCPQ_SHIFT },
>                 { GMAC_RXQCTRL_UPQ_MASK, GMAC_RXQCTRL_UPQ_SHIFT },
>                 { GMAC_RXQCTRL_MCBCQ_MASK, GMAC_RXQCTRL_MCBCQ_SHIFT },
>         };
>
>         value = readl(ioaddr + GMAC_RXQ_CTRL1);
>
>         /* routing configuration */
>         value &= ~route_possibilities[packet - 1].reg_mask;
>         value |= (queue << route_possibilities[packet-1].reg_shift) &
>                  route_possibilities[packet - 1].reg_mask;
>
>
> Calling the function with e.g. packet == 0 will lead to interesting stuff,
> so the smatch warning is absolutely warranted.

Notice that stmmac_mac_config_rx_queues_routing() checks for
packet == 0x0 and if its true then should never call
rx_queue_routing, check [1] ...

>
>
> Looking where this function is used:
>
> static const struct stmmac_ops dwmac4_ops = {
>         ...
>         .rx_queue_routing = dwmac4_tx_queue_routing,
>
> Mixing rx and tx.. is this really correct?

It should be dwmac4_rx_queue_routing.

>
>
>
> Looking where the rx_queue_routing function is used:
> git grep rx_queue_routing
> stmmac_main.c:  if (rx_queues_count > 1 && priv->hw->mac->rx_queue_routing)
>
> it is just referenced in a single place, and we only check if function is
> non-NULL, we never even call the function, so right now it is just unused
> code.

[1] Another typo. You can see that in function
stmmac_mac_config_rx_queues_routing() we are calling
rx_queue_prio instead of rx_queue_routing ...

Best Regards,
Jose Miguel Abreu

>
>
> Regards,
> Niklas